Electron-emitting cathode and method of making it



May 8, 1928.

. v 1,668,734 E. E. SCHUMACHER ELECTRON EMITTING CATHODE AND METHOD OF MAKING IT Filed July 12, 1923 Patented May 8, 1.?28.

'UNITED STATES 4 1,668,734 PATENT orrica.

E. SOHUMAGHER, OF EAST OBANGE, NEW JERSEY, ASSIGNOR TO WES'I'EBN' ELECTRIC COHPANY, INCORPORATED, OF NEW YORK, 11'. Y., A CORPORATION 01' NEW YORK.

ELECTRON-EMITTING GATHODE ,AND METHODv OF MAKING 1'1.

Application filed m 12,

This invention relates to electron emitting cathodes and has for its object a filament of high thermionic activity.

This object is attained by combining a thermionically active material with a metallie filament. To do, this, the filament is heated to at least a red heat, preferably in vacuum, and finely powdered thermionically active material isbrought' into contact with the surface of the filament. The powder adheres to the filament and is incorporated therewith to form a highly active and stable cathode. A filament of tungsten, molybdenum or the like may have alloyed, by this 'method, a thermionically active metal, such as uranium or the metals of the cerium group. Cathodes having these constituents possess a thermionic activity comparable to that of a platinum nickel filament coated with alkaline earth oxides.

Referring now to'the drawing, the sin le figure thereof discloses an apparatus. or

treating filaments.

Within an evacuated vessel 10 is supported, by' means of leading-in wires 11 and 12 sealed in the vessel, a metallic filament 13, which is to be treated. Also contained within the vessel 10 is a supply 14 of a thermionically active material to be combined with the filament 13, the material being in finely powdered condition. A battery 15 is connected to the leading-in wires 11 and 12 to provide heating current for the filament. After the filament has been mounted within the vessel and the powdered thermionically active material introduced, the'vessel is evacuated. The filament 13 is then heated'to a red heat, or hotter if necessary, and the vessel 10 shaken to bring the particles of the thermionically active 'material into contact with the surface of the filament. The particles contacting with the filament adhere thereto and combine therewith to form a composite filament. After sufficient of the powdered material has been combined with the filament, the current is cut oil, the vessel opened and the filament removed therefrom. The filament is then combined with the other elements of an electron discharge device and sealed within an evacuated vessel in the usual manner.

This method of roducing thermionic cathodes is particular adapted for use in forming an alloy li ament of tungsten,

1923. Serial No. 850,985.

molybdenum or other metals capable of being formed into a filamentary conductor and thermionically highly active metals, such i as cerium, lanthanum, praseodymium, neodymium, Samarium or uranium. The latter metals may be introduced into the vessel 10 in the 'form of filings; The metallic filament is heated to a sufliciently high temperature so "that wheni the filings come in contact therewith, they combine therewith to form an alloy. The temperature of the filament may range from a dull red heat up to white hot, depending upon the particular filament used and the extent of oxidation of the metal filings. If the filings are considerably oxidiae the filament has to be more highly heated than otherwise. An alloy filament formed of tun stem or molybdenum, and any! one of the a ore-mentioned thermionically active metals, possess a thermionic activity comparable to that of a platinum nickel filament coated with alkaline earth oxides. Although this invention has been disclosed as particularly'adapted for forming metalhc filaments, the method employed is adapted for use wherever it, is desired to combine any thermionically active material with a conductive core. For example, this method is also capable 05 use in the production of metallic filaments coated with alkaline earth oxides. A filament of tungsten, tantalum, molybdenum, or the like, may have applied thereto a coatin oxides or othersnnilar alkaline earth oxides by providing a supply of the coating mateterial within the vessel 10 and shaking the latter to bring the powdered material into contact with the heated filament; The particles will adhere to the filament and form therefor a thermionically highly active coating;

The selection of materials to be combined,

of barium and strontium 4 according to this method, is therefore not limited to the particular materials above enumerated and various materials. may be utilized without departing in any way from the spirit of the invention, as set forth in v the appended claims.

What is claimed is:

1. The method of producing a thermionic cathode which comprises supporting a metal; lic filament in an evacuated vessel containing powdered thermionically active material, passing heating current through said filament, and agitating said vessel to bring said thermionically active material into contact with said heated filament.

2. The method of producing a thermionic 6 cathode which comprises heatm a metallic filament and bringing powdered the influence of gravity only. 8. A method, of producing a thermionic thermionicalliy active material into contact therewith m or cathode which comprises supporting a fila- 10 ment in a vessel containin' thermlonically active material, heating said filament and bringing said thermionically active material into contact with said filament under the influence of gravity onl In witness whereof, {hereunto subscribe my name this 3rd da of Jul A. D. 1923.

EARLE SC CHER. 

